Display screen or portion thereof with a graphical user interface



The sole FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The outermost broken line in the sole FIGURE shows the display screen or portion thereof and forms no part of the claimed design. The other broken line showing of an icon illustrates portions of the graphical user interface that forms no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 